Silica-type micropowder has been used in a number of industrial fields in order to inhibit the solidification of powders and increase fluidity.
One such application concerns those resin powders whose use requires that they become electrostatically charged, such as the dry toners in electrophotographic copiers. In such cases, the charging properties of any additive are an important consideration. In recent years, this field has witnessed increased demand for positively-charging toner in conjunction with advances in the development of organic photosemiconductors, and it is thought desirable that any additive for improving the fluidity in this regard would itself be positively chargeable.
One method for obtaining such a positively-charging additive is the method disclosed in Japanese Patent Publication Number 53-22447 [22,447/78]. In Japanese Patent Publication Number 53-22447, an electrostatic developer is prepared by treating a metal oxide powder with an aminoalkylalkoxysilane. The present inventor carried out a detailed investigation of whether it would be useful to attempt to increase the fluidity of positively-charging resin powders through the treatment of silica-type microparticles with the aminoalkylalkoxysilanes exemplified in the aforementioned publication. However, the treated silica obtained as a result did not have good properties as a fluidity improver for positively-charging resin powders.
Thus, the obtained treated silica was in many cases hydrophilic, and, when added to a positively-charging resin powder, the fluidity declined in a short period of time due to moisture absorption. In other cases, while the treated silica was initially hydrophobic, moisture absorption nevertheless occurred during long-term storage due to an unsatisfactory hydrophobicity, and the fluidity again declined in conjunction with this.
Consequently, the present inventor directed his research toward the development of an excellent fluidity improver for positively-charging resin powders, and achieved the present invention as a result.